Lymphatic System

Question 1

Explain the hydrostatic pressure and oncotic pressure effect in a capillary bed and how this allows tissue fluid to enter lymphatic capillary

Answer 1

• In a capillary bed, the hydrostatic pressure of the capillaries in the arteriole side drive fluid into the interstitial space
• Oncotic pressure on the venule side is able to absorb some of the water back
• However little proteins can enter the interstitial space through the small gaps in the capillary
  
  • This takes water with it so not all fluid can be absorbed
• Net filtration of fluid ≠ net reabsorption of fluid
• Tissue fluid (fluid in interstitium) enters the lymphatic capillary
  
  • Walls of lymphatic capillary more porous than blood capillary to allow tiny proteins to enter

Question 2

What material enters lymph

Answer 2

• Tissue fluid, small proteins, damaged cells, bacteria, cancer cells, lipids (chylomicrons from gut lymphatics)

Question 3

How much lymphatic fluid is produced per day

Answer 3

• 3-4 L of lymphatic fluid produced per day

- Amount of fluid filtered out of blood capillaries exceeds what is absorbed by 4L/day

Question 4

Explain passive and intrinsic constriction in lymphatic system

Answer 4

• No central pump but has valves
• Passive constriction - lymph vessels run next to muscle or artery to push fluid
  
  • Valves only allow single direction flow
• Intrinsic constriction - when area fills up, own walls squeeze fluid

Question 5

Explain how a low pressure system in the lymphatics allows fluid to join the blood

Answer 5

• Low pressure system - higher than venous circulation at point of joining
• Lowest pressure of venous circulation just before it enters heart
• Thoracic duct and right lymphatic duct drain into left and right subclavian veins

Question 6

Briefly state the structure of lymph nodes

Answer 6

• Tough fibrous outer capsule

- Reticular connective tissue inside (candy floss)

Question 7

Explain the role of lymph nodes

Answer 7

• Immune surveillance and defense
• Highly organized centres of immune cells - lymphocytes
• Lymph draining into lymph nodes may contain pathogens
  
  • All substances transported in lymph pass through ≥ 1 lymph node
  • Physical filter, phagocytic filter
  • Full of lymphocytes - activate and proliferate in response to antigens

Question 8

What is lymphedema

Answer 8

Abnormal collection of protein-rich fluid causing tissue swelling due to compromised lymphatic system

Question 9

State causes of lymphedema

Answer 9

• Removal or enlargement of lymph nodes
• Infections
• Damage to lymphatic system - eg. Cancer treatments
• Lack of limb movement - muscle contraction assists lymph fluid movement
• Congenital - Milroy’s syndrome

Question 10

What is lymphadenopathy

Answer 10

• Abnormal size or number of lymph nodes

- Pathogens can enter alongside interstitial fluid

Question 11

What are causes of lymphadenopathy

Answer 11

• Enlarged lymph nodes mainly caused by infection
  
  • Tender, mobile
• Can also be caused by malignancy
  
  • Hard, matted, non-tender

Question 12

Distinguish between regional and terminal lymph nodes

Answer 12

• Regional - drain specific areas

- Terminal - receive drainage from number of regional nodes

Question 13

How are regional and terminal lymph nodes separated in the head and neck

Answer 13

• Superficial (regional) and deep (terminal) lymph nodes separated by investing layer of deep cervical fascia of neck
• Some deep lymph nodes lie within carotid sheath

Question 14

State the major superficial (regional) lymph nodes of the head

Answer 14

• Submental
• Submandibular
• Pre-auricular
• Post-auricular
• Occipital
• Superficial: EJV
• Posterior: EJV
• Anterior: EJV

Question 15

State the major deep (terminal) lymph nodes of the head

Answer 15

• Jugulo-digastric
• Jugulo-omohyoid
• Suptraclavicular lymph nodes

Question 16

Where does the supraclavicular lymph node drain from

Answer 16

• Supraclavicular lymph nodes oversee transport of lymph from thoracic cavity and abdomen
• Left node - abdomen and thorax - Virchow’s node
• Right node - mid section chest, oesophagus and lungs

Question 17

Where does the jugulo-digastric node drain from

Answer 17

• Jugulo-digastric node drains the palatine tonsil, oral cavity and tongue
• Often swollen and tender in tonsillitis

Question 18

Where does the jugulo-omohyoid node drain from

Answer 18

Jugulo-omohyoid drains the tongue, oral cavity, trachea, oesophagus, thyroid gland

Question 19

What is the Waldeyer’s Ring

Answer 19

A circle of protective lymphoid tissue at the upper ends of the respiratory and alimentary canal

Question 20

State the location of the structures which form Waldeyer’s Ring

Answer 20

• Pharyngeal tonsil - nasopharynx behind nose and soft palate
  
  • Also known as adenoids tonsil
• 2 palatine tonsils - located on the left and right of the oropharynx
  
  • Enlarged in tonsillitis
• 2 tubal tonsils - located on the left and right at the auditory tube opening
• Lingual tonsil - posterior 1/3 of tongue

Question 21

Explain how adenoids tonsil infection can affect hearing

Answer 21

Enlargement and infection can spread through the auditory tube and affect hearing from the middle ear